Technical Field
The present invention relates to a folder-gluer, and more particularly to a folder-gluer for folding and gluing a corrugated paperboard sheet having four panels and a joint flap.
Background Art
Generally, a corrugated paperboard box making machine is configured to perform slotting and creasing to thereby form, in a corrugated paperboard sheet, a plurality of slots and crease lines each extending in a conveyance direction. The corrugated paperboard sheet is designed to be formed as a box, i.e., has four panels and a joint flap. A folder-gluer is one processing unit comprised in the corrugated paperboard box making machine, and configured to fold endmost two of the four panels of the corrugated paperboard sheet by 180 degrees, and glue one of the folded panels to the joint flap. During conveyance of the corrugated paperboard sheet at high speed, each of the two endmost panels is folded through contact between an outside surface of the panel and a bending bar or bending belt.
With reference to FIGS. 17 to 19, one example of a conventional folder-gluer will be described. A conventional folder-gluer 90 comprises: a frame 92; a conveyance device (upper conveyor belt and a lower conveyor belt) 94 for conveying a corrugated paperboard sheet SS comprising four panels P1 to P4; a first bending station 96 for bending each of the endmost panels P1, P4 of the corrugated paperboard sheet SS from 0 degree to about 90 degrees; and a second bending station (not illustrated) for bending each of the endmost panels from about 90 degrees to 180 degrees.
In order to bend the two endmost panels P1, P4 of the corrugated paperboard sheet SS from 0 degree to about 90 degrees, the first bending station 96 illustrated in FIGS. 17 and 18 employs a pair of bending bars 98 configured to come into contact with respective outside surfaces of the two endmost panels P1, P4, and a pair of bending plates 100 each configured to allow a respective one of the two endmost panels to be bent along an associated crease line. Each of the bending plates 100 is arranged such that a distal end (upper end) thereof is located slightly inwardly in a width direction with respect to a position of the crease line along which the panel P1, P4 is to be bent. The reason is as follows. Since the corrugated paperboard sheet SS has a certain thickness, if the distal end of the bending plate 100 is located just at the position of the crease line, the corrugated paperboard sheet SS bulges along with the bending, the distal end is pinched between edges of the bulged portion of the corrugated paperboard sheet SS, and resulting friction makes it impossible to successfully convey the corrugated paperboard sheet SS. The above arrangement is intended to prevent the occurrence of this situation.
As above, there is a slight distance between the distal end of the bending die plate 100 and the position of the crease line, so that, due to contact frictional resistance between respective ones of the bending bars 98 and conveyance-directional leading edge regions (downstream edge regions) of the two endmost panels P1, P4 of the corrugated paperboard sheet SS being conveyed, a fold line of each of the two endmost panels is shifted inwardly in the width direction with respect to the position of the crease line, in the leading edge region of the corrugated paperboard sheet SS, and thereby each of the two endmost panels P1, P4 has a posture where it is inclined outwardly in the width direction (see FIG. 18). Then, the corrugated paperboard sheet having the two endmost panels bent in the inclined posture is introduced into a last-half (downstream) zone of the folder-gluer, and each of the two endmost panels is further bent from about 90 degrees to 180 degrees, while being guided by a corresponding one of two sets of a plurality of gauge rollers (guide rollers) disposed on both sides of the corrugated paperboard sheet. In this case, the bending is progressed while each of the two endmost panels P1, P4 is kept in the inclined posture, so that a box is formed such that the fold lines of the two endmost panels are inclined (skewed) in a fishtail shape toward an upstream side in the conveyance direction. This “fishtail” problem is more likely to occur, as the corrugated paperboard sheet has a larger box depth dimension in the conveyance direction.
FIG. 19 illustrates a folded corrugated paperboard sheet SS produced by the above folder-gluer, wherein the fishtail occurs in this corrugated paperboard sheet SS. Specifically, a gap between edge regions of the two endmost panels on a downstream side in the conveyance direction is “−A”, and a gap between edge regions of the two endmost panels on the upstream side is “B”, so that a difference between the upstream-side and downstream-side gaps between the two endmost panels is “A+B”. That is, in the folded corrugated paperboard sheet SS, the fold lines obliquely extend in a direction from the downstream side to the upstream side to form a fishtail shape.
With a view to preventing the occurrence of the fishtail in a corrugated paperboard sheet, various devices have heretofore been invented. For example, a folder-gluer disclosed in JP 4493052 B (Patent Document 1) comprises a pair of pressing members which are arranged in a width direction perpendicular to a conveyance direction of a corrugated paperboard sheet being folded, and configured to press connection regions of two endmost panels of the corrugated paperboard sheet, while determining a timing of the pressing, to thereby correct the fishtail.